Such examination devices comprise an objective for observing the sample. If, with the aid of the objective, for example a sample in the sample carrier is viewed from below through a sample carrier bottom transparent to observation radiation, the given constellation of the refraction indices has an adverse effect on the course of the radiation path, in particular in high numeric objectives. Different refraction indices occur at the transitions between the exit lens of the objective and the ambient air as well as between the bottom of the sample carrier and the medium arranged between the objective and the sample carrier bottom.
In particular confocal microscopes used for high-throughput screening require a very small focus. This is necessary since in high-throughput screening samples with small volumes in the μl-range are examined. Since the amount of radiation emitted by the sample and detected by the objective (collection efficiency) has a large influence on the measuring time, the aperture of the objective must be as high as possible. This is of importance in particular in high-throughput screening since the measuring time is one of the crucial parameters.
Usually, an immersion liquid with a refraction index of >1 is applied to the exit lens of the objective. Such an examination device, where the immersion liquid is automatically supplied, is known from WO 02/093232. The objective of the device is arranged at such a small distance to a sample carrier that the immersion liquid applied to the objective is held by capillary forces in a gap defined between the objective and an outer surface of a sample carrier wall. Alternatively, the immersion liquid may be supplied by vertically and/or horizontally moving the objective for the purpose of applying, for example with a pipette, an immersion medium, such as distilled water, to the objective without abutting on the sample carrier. The objective of the described device is surrounded by a collection means for receiving excess immersion medium. This arrangement is intended to prevent the objective from becoming fouled by particles adhering to the glass bottom.
It is a drawback of such an examination device that the collection means can only be of a very small size due to shortage of space. This leads to difficulties with regard to discharge of the immersion medium in the collection means. The excess immersion medium normally forms individual drops in the collection means, said drops being difficult to draw off the collection means by suction via a single suction opening. Over time, the drops become increasingly larger such that there is the risk of a drop becoming that large that the immersion medium flows over the edge of the collection means. In particular when the sample carrier is subjected to high acceleration forces, as in the case of measuring time reduction in high-throughput screening, there is the risk of individual drops of the immersion medium adhering to the cover slip and falling down later.
It is an object of the invention to provide a device and a method for examining chemical and/or biological samples, and an objective cap which allows immersion liquid to be reliably and automatically supplied and discharged.